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Refrigerant leak rate statistics that I've seen are typically figured on a flat yearly basis as in #/yr. The formula you posted would give you a rate based on the length of time since refrigerant was last added to the system. Rather than giving you a #/yr number, it gives you the pounds per number of years since last added.....which is meaningless if you're trying to track this system's leak rate against other similar systems.

Some years ago FMI (Food Marketing Institute) did a national study of refrigerant leak rates in supermarkets among member chains to develop a handle on just what the typical loss per year is and came up with about 35%/yr. It was based on the amount of refrigerant lost per year and the total refrigerant charge.

I would use a formula that looks more like: (# added in last year) / (# full charge X 100). That way, a system with say a 100# full charge that had 10 lbs added in a year's time would have a 10% yearly leak rate. If this same system lost its complete charge twice in one year the leak rate would be 200%. Those numbers would be meaningful statistics to have.

You can play with the statistics to make them give you what you need. Let's say the above system has had no leak history and over a period of 30 days 10 lbs are added. You then also have a leak rate of 10% per month. With this you can extrapolate out to one year and get a yearly rate of 120% if this current loss rate continues.

sounds good ice, but my company wants to have a per leak percentage figure. I work on rack sys. that may have up to 800 pound plus charges, multiple sys. on the rack so we have more leak possibilities. I like what you have there and am wondering if I take your formula and take the answer and divide it by the number of days since last charge, than wouldn't that give me a leak % per day for just the number of days until the leak was fixed?
ex. 100 lb sys leaked 10 lb over 30 days. than it would be .33% leak rate per day
just asking and I thank you for the input was very helpful.